key: cord-310691-6danlh8h
authors: Ma, Simin; Lai, Xiaoquan; Chen, Zhe; Tu, Shenghao; Qin, Kai
title: Clinical Characteristics of Critically Ill Patients Co-infected with SARS-CoV-2 and the Influenza Virus in Wuhan, China
date: 2020-05-26
journal: Int J Infect Dis
DOI: 10.1016/j.ijid.2020.05.068
sha: 
doc_id: 310691
cord_uid: 6danlh8h

OBJECTIVE: To delineate the clinical characteristics of critically ill COVID-19 patients co-infected with influenza. METHODS: In this study, we included adult patients with laboratory-confirmed COVID-19 form Tongji Hospital (Wuhan, China), with or without influenza, and compared their clinical characteristics. RESULTS: Among 93 patients, 44 died and 49 were discharged. Forty-four (47.3%) were infected with influenza virus A and 2 (2.2%) with influenza virus B. Twenty-two (50.0%) of the non-survivors and 24 (49.0%) of the survivors were infected with the influenza virus. Critically ill COVID-19 patients with influenza were more prone to cardiac injury than those without influenza. For the laboratory indicators at admission, white blood cell counts, neutrophil counts, levels of tumor necrosis factor-α, D-dimer value, and proportion of elevated creatinine were higher in non-survivors with influenza than in those without influenza. CONCLUSION: The results showed a high proportion of COVID-19 patients were co-infected with influenza in Tongji Hospital, with no significant difference in the proportion of co-infection between survivors and non-survivors. The critically ill COVID-19 patients with influenza exhibited more severe inflammation and organ injury, indicating that co-infection with the influenza virus may induce an earlier and more frequently occurring cytokine storm.

The World Health Organization (WHO) named the coronavirus disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as 2019 novel coronavirus disease and declared it as a pandemic. Similar to the influenza virus, SARS-CoV-2 is commonly transmitted through respiratory droplets and contact. The world's population is generally susceptible to SARS-CoV-2 infection.

Most COVID-19 patients show mild influenza-like symptoms, such as fever, cough, and fatigue. However, approximately 5% of patients rapidly progress to acute respiratory distress syndrome (ARDS), septic shock, and multiple organ failure and are admitted to intensive care units. The COVID-19-associated mortality rate in China is approximately 2.3% (Guan et al. 2020; Novel Coronavirus Pneumonia Emergency Response Epidemiology Team 2020) . To date, no studies have reported on critically ill COVID-19 patients who also present with influenza. Human cases of influenza in Wuhan occur in winter most often (He and Tao 2018; Wang et al. 2018) , which overlaps the peak of COVID-19 in Wuhan. We speculated whether co-infection with SARS-CoV-2 and the influenza virus existed. And if so, the influence of this co-infection on clinical features needs to be investigated.

The Southern hemisphere is yet to enter its flu season for the year and in many of these countries the incidence of COVID-19 is still increasing. Meanwhile, many Western hemisphere countries are still experiencing COVID-19 outbreaks. And a great many countries around the world will be looking to start planning for flu season 2020/21 with many public health experts warning of the need to avoid second peaks of COVID-19 during flu season. Therefore, answering the above questions is crucial for the formulation of treatment strategies to manage co-infection with SARS-CoV-2 and the influenza virus. In the present study, we extracted the clinical data for 95 patients J o u r n a l P r e -p r o o f with laboratory-confirmed COVID-19 from Tongji Hospital (Wuhan) and discussed the clinical characteristics of critically ill COVID-19 patients co-infected with influenza. Our results may provide new insights into the treatment and control of co-infection with SARS-CoV-2 and the influenza virus.

The study was conducted among 95 adult patients with laboratory-confirmed COVID-19 (including 50 discharged cases and 45 non-survivors) discharged/died in and interleukin-6 [IL-6], and respiratory virus-specific IgM antibodies), detailed medication, and tests for SARS-CoV-2 from respiratory tract specimens (including nasopharyngeal swabs, bronchoalveolar lavage fluid, sputum, or bronchial aspiration fluid). Specimen collection and lung CT scanning were completed for all patients within 24 hours of admission.

A confirmed COVID-19 case was defined as a positive result in a RT-PCR assay of nasal and pharyngeal swab specimens according to WHO guidelines. On receipt of the samples, viral RNA extraction was performed using a Magnetic Viral RNA/DNA Extraction Kit (Tianlong, Xi'an, China) following the manufacturer's instructions. This was followed by PCR screening for the specific detection of SARS-CoV-2 using a commercial kit (Tianlong). A cycle threshold value (Ct-value) ≤37 was defined as a positive test based on the recommendation of the National Institute for Viral Disease Control and Prevention (China). 

Statistical analysis was performed using SPSS 20.0. Continuous variables were expressed as means ± standard deviation (SD) using the Student's t-test or as medians and interquartile range (IQR) using the Mann-Whitney U test. Categorical variables were expressed as numbers (%) and compared by the χ 2 test or Fisher's exact test. P< 0.05 was considered significant.

Of the 95 COVID-19 patients, 44 were infected with influenza virus A, 2 with influenza virus B, 1 with adenovirus, 1 with parainfluenza; 47 were uninfected. A total of 93 patients were finally included, 46 (49.5%) of whom were infected with influenza virus A or B (classified as the flu group), while the rest (47; 50.5%) were uninfected (classified as the non-flu group). Of these 93 patients, 44 were non-survivors and 49 were discharged. Twenty-two (50.0%) non-survivors and 24 (49.0%) survivors were infected with the influenza virus. There was no significant difference in the proportion J o u r n a l P r e -p r o o f of patients co-infected with SARS-CoV-2 and the influenza virus between survivors and non-survivors.

The median age of the 93 patients was 67.0 years (IQR 54.0-72.0) and females accounted for 45.2% of the total number of patients (Table 1 ). The median time from illness onset to admission was 12.0 days (IQR 7.0-16.0) ( Table 1) . Chronic diseases were found in 53.8% of the patients, with hypertension being the most common, followed by diabetes and coronary disease ( Table 1) . The most common symptoms on admission were fever, cough, and dyspnea, followed by chest distress/chest pain and fatigue ( Table 1 ). The most common complication was ARDS, followed by acute cardiac injury, acute kidney injury, and liver dysfunction. Among the non-survivors, the incidence of acute cardiac injury was significantly higher in the flu group (86.4%) than in the non-flu group (54.5%) (P< 0.05) ( Table 2) .

Among the 93 patients, there was a significant difference in the proportion of patients with D-dimer levels >5μg/mL (ten times the normal D-dimer value) between the flu group (38.6%) and the non-flu group (11.4%) (P< 0.01), but no difference in white blood cell counts, neutrophil counts, lymphocyte counts, or levels of CRP, ALT, AST, LDH, creatinine, cTnI, NT-proBNP, TNF-α,and IL-6 (P> 0.05) (data not shown).

Among the non-survivors, the white blood cell count, neutrophil count, TNF-α, D-dimer value, proportion of patients with D-dimer levels >5μg/mL, and proportion of patients with elevated creatinine levels were higher in the flu group than in the non-flu group (P< 0.05) ( Table 3) Most patients with severe COVID-19 exhibit substantially elevated serum levels of pro-inflammatory cytokines, characterized as cytokine storm (Cao 2020; Mehta et al. 2020) . Elevated cytokines also mediate extensive pulmonary pathology, leading to J o u r n a l P r e -p r o o f massive infiltration of neutrophils and macrophages (Cao 2020) . Neutrophil counts are increased in both the peripheral blood (Wang et al. 2004 ) and lung (Nicholls et al. 2003) among critically ill patients with severe acute respiratory syndrome. Extensive pulmonary infiltration of neutrophils in patients with influenza induces lung tissue injury and worsens the disease (Kulkarni et al. 2019 ). In our study, neutrophil and cytokine levels were generally elevated among the non-survivors, and the increment was more apparent among the non-survivors with influenza. Co-infection with the influenza virus may further enhance neutrophil activation, thereby contributing not only to an excessive immune response against the virus, but also contributing to the development of a cytokine storm.

Studies have reported that elevated D-dimer levels are a risk factor for death in COVID-19 patients (Wu et al. 2020a; Zhou et al. 2020) . We also found that the D-dimer levels of non-survivors were substantially higher than those of survivors.

Among the non-survivors, the D-dimer value was higher among patients with influenza than in those without influenza, which may have been due to local vascular injury, ischemia, and thrombosis caused by a viral infection-associated cytokine storm (Davidson and Warren-Gash 2019) . Our results further confirmed that co-infection with the influenza virus may induce an earlier and more severe cytokine storm in critically ill COVID-19 patients, leading to serious complications such as shock, ARDS, fulminant myocarditis, acute kidney injure or multiple organ failure (Cao 2020; Ruan et al. 2020; Wu et al. 2020a; Zhou et al. 2020) .

The current research had some limitations. First, the results of serological tests may be false-negative, especially within one week of infection or reinfection; or they may be false-positive due to long-term infections or carrier states. Second, we were unable to determine the strains of influenza, and the infecting strain might affect the J o u r n a l P r e -p r o o f clinical characteristics. Third, the included cases originated from Wuhan, but differences in races and influenza strains among different countries may make COVID-19 patients with influenza present different clinical characteristics. In addition, the number of included cases was small, and other factors such as gender, age, chronic disease, and time from illness onset to admission may have affected the results of this study.

Under the background of COVID-19 global pandemic, the number of patients co-infected with SARS-CoV-2 and the influenza virus in some countries may increase as the flu season approaches. The clinical research of this co-infection, especially in the critically ill patients, will benefit global control efforts for 2020-2021. Researches on different regions, races, age brackets, and influenza strains can reveal the epidemiological and clinical characteristics of co-infected patients more accurately, which requires larger sample sizes from multiple countries. Furthermore, research from larger sample could contribute to unveiling whether this co-infection is the higher risk for severe disease or death associated with COVID-19.

To the best of our knowledge, this is the first study of co-infection with SARS-CoV-2 and the influenza virus among critically ill COVID-19 patients. The results showed that a high proportion of COVID-19 patients were co-infected with influenza in Tongji Hospital. Co-infection with SARS-CoV-2 and the influenza virus may lead to a much earlier occurrence of the cytokine storm and organ damage in critically ill COVID-19 patients. Our results suggest that detection of the influenza virus should be considered in patients with COVID-19, and that treatment strategies of anti-influenza virus and dampening inflammatory responses may be helpful for critically ill patients co-infected with SARS-CoV-2 and the influenza virus. 

The authors declare no conflict of interest.

The submission of manuscript entitled "Clinical Characteristics of Critically Ill Patients Co-infected with SARS-CoV-2 and the Influenza Virus in Wuhan, China" to "International Journal of Infectious Diseases" for publication has been approved by all of the authors and by the institution where the work was carried out. All authors agree to abide by the journal's editorial policies and publishing ethics. There are not any competing interests on submission of this manuscript. J o u r n a l P r e -p r o o f J o u r n a l P r e -p r o o f 

White blood cell count (×10 9 /L) 9.5(6.1, 13.6) 12.9(8.9, 15.4) 7.4(5.1, 11.0) 0.01

Neutrophil count (×10 9 /L) 8.7(5.1, 12.6) 11.5(7.5, 13.6) 6.5(4.0, 10.0) 0.01

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Excessive neutrophil levels in the lung underlie the age-associated increase in influenza mortality

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Data are expressed as the median (IQR) or n/N (%), p-values are from the Mann-Whitney U test, χ² test or Fisher's exact test. COVID-19=coronavirus disease 2019

AST=aspartate aminotransferase; NT-proBNP=amino-terminal pro-brain natriuretic peptide precursor

We thank the staff members of Tongji Hospital for the management of patients.J o u r n a l P r e -p r o o f